Chemokine Transfer by Liver Sinusoidal Endothelial Cells Contributes to the Recruitment of CD4+ T Cells into the Murine Liver

Angiocrine signaling in sinusoidal homeostasis and liver diseases

The hepatic sinusoids are composed of liver sinusoidal endothelial cells (LSECs), which are surrounded by hepatic stellate cells (HSCs) and contain liver-resident macrophages called Kupffer cells, and other patrolling immune cells. All these cells communicate with each other and with hepatocytes to maintain sinusoidal homeostasis and a spectrum of hepatic functions under healthy conditions. Sinusoidal homeostasis is disrupted by metabolites, toxins, viruses, and other pathological factors, leading to liver injury, chronic liver diseases, and cirrhosis. Alterations in hepatic sinusoids are linked to fibrosis progression and portal hypertension. LSECs are crucial regulators of cellular crosstalk within their microenvironment via angiocrine signaling. This review discusses the mechanisms by which angiocrine signaling orchestrates sinusoidal homeostasis, as well as the development of liver diseases. Here, we summarise the crosstalk between LSECs, HSCs, hepatocytes, cholangiocytes, and immune cells in health and disease and comment on potential novel therapeutic methods for treating liver diseases.

Angiocrine Signaling in Sinusoidal Health and Disease

Liver sinusoidal endothelial cells (LSECs) are key players in maintaining hepatic homeostasis. They also play crucial roles during liver injury by communicating with liver cell types as well as immune cells and promoting portal hypertension, fibrosis, and inflammation. Cutting-edge technology, such as single cell and spatial transcriptomics, have revealed the existence of distinct LSEC subpopulations with a clear zonation in the liver. The signals released by LSECs are commonly called "angiocrine signaling." In this review, we summarize the role of angiocrine signaling in health and disease, including zonation in healthy liver, regeneration, fibrosis, portal hypertension, nonalcoholic fatty liver disease, alcohol-associated liver disease, aging, drug-induced liver injury, and ischemia/reperfusion, as well as potential therapeutic advances. In conclusion, sinusoidal endotheliopathy is recognized in liver disease and promising preclinical studies are paving the path toward LSEC-specific pharmacotherapies.

A narrative review: CXC chemokines influence immune surveillance in obesity and obesity-related diseases: Type 2 diabetes and nonalcoholic fatty liver disease

Adipose tissue develops lipids, aberrant adipokines, chemokines, and pro-inflammatory cytokines as a consequence of the low-grade systemic inflammation that characterizes obesity. This low-grade systemic inflammation can lead to insulin resistance (IR) and metabolic complications, such as type 2 diabetes (T2D) and nonalcoholic fatty liver disease (NAFLD). Although the CXC chemokines consists of numerous regulators of inflammation, cellular function, and cellular migration, it is still unknown that how CXC chemokines and chemokine receptors contribute to the development of metabolic diseases (such as T2D and NAFLD) during obesity. In light of recent research, the objective of this review is to provide an update on the linkage between the CXC chemokine, obesity, and obesity-related metabolic diseases (T2D and NAFLD). We explore the differential migratory and immunomodulatory potential of CXC chemokines and their mechanisms of action to better understand their role in clinical and laboratory contexts. Besides that, because CXC chemokine profiling is strongly linked to leukocyte recruitment, macrophage recruitment, and immunomodulatory potential, we hypothesize that it could be used to predict the therapeutic potential for obesity and obesity-related diseases (T2D and NAFLD).

Gene Expression Changes in Cytokine and Chemokine Receptors in Association with Melanoma Liver Metastasis

Cytokines and chemokines (chemotactic cytokines) are soluble extracellular proteins that bind to specific receptors and play an integral role in the cell-to-cell signaling network. In addition, they can promote the homing of cancer cells into different organs. We investigated the potential relationship between human hepatic sinusoidal endothelial cells (HHSECs) and several melanoma cell lines for the expression of chemokine and cytokine ligands and receptor expression during the invasion of melanoma cells. In order to identify differences in gene expression related to invasion, we selected invasive and non-invasive subpopulations of cells after co-culturing with HHSECs and identified the gene expression patterns of 88 chemokine/cytokine receptors in all cell lines. Cell lines with stable invasiveness and cell lines with increased invasiveness displayed distinct profiles of receptor genes. Cell lines with increased invasive capacity after culturing with conditioned medium showed a set of receptor genes (CXCR1, IL1RL1, IL1RN, IL3RA, IL8RA, IL11RA, IL15RA, IL17RC, and IL17RD) with significantly different expressions. It is very important to emphasize that we detected significantly higher IL11RA gene expression in primary melanoma tissues with liver metastasis as well, compared to those without metastasis. In addition, we assessed protein expression in endothelial cells before and after co-culturing them with melanoma cell lines by applying chemokine and cytokine proteome arrays. This analysis revealed 15 differentially expressed proteins (including CD31, VCAM-1, ANGPT2, CXCL8, and CCL20) in the hepatic endothelial cells after co-culture with melanoma cells. Our results clearly indicate the interaction between liver endothelial and melanoma cells. Furthermore, we assume that overexpression of the IL11RA gene may play a key role in organ-specific metastasis of primary melanoma cells to the liver.

Tissue CD14+CD8+ T cells reprogrammed by myeloid cells and modulated by LPS

The liver is bathed in bacterial products, including lipopolysaccharide transported from the intestinal portal vasculature, but maintains a state of tolerance that is exploited by persistent pathogens and tumours1-4. The cellular basis mediating this tolerance, yet allowing a switch to immunity or immunopathology, needs to be better understood for successful immunotherapy of liver diseases. Here we show that a variable proportion of CD8+ T cells compartmentalized in the human liver co-stain for CD14 and other prototypic myeloid membrane proteins and are enriched in close proximity to CD14high myeloid cells in hepatic zone 2. CD14+CD8+ T cells preferentially accumulate within the donor pool in liver allografts, among hepatic virus-specific and tumour-infiltrating responses, and in cirrhotic ascites. CD14+CD8+ T cells exhibit increased turnover, activation and constitutive immunomodulatory features with high homeostatic IL-10 and IL-2 production ex vivo, and enhanced antiviral/anti-tumour effector function after TCR engagement. This CD14+CD8+ T cell profile can be recapitulated by the acquisition of membrane proteins-including the lipopolysaccharide receptor complex-from mononuclear phagocytes, resulting in augmented tumour killing by TCR-redirected T cells in vitro. CD14+CD8+ T cells express integrins and chemokine receptors that favour interactions with the local stroma, which can promote their induction through CXCL12. Lipopolysaccharide can also increase the frequency of CD14+CD8+ T cells in vitro and in vivo, and skew their function towards the production of chemotactic and regenerative cytokines. Thus, bacterial products in the gut-liver axis and tissue stromal factors can tune liver immunity by driving myeloid instruction of CD8+ T cells with immunomodulatory ability.

Endothelial Cell Dysfunction and Nonalcoholic Fatty Liver Disease (NAFLD): A Concise Review

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. It is strongly associated with obesity, type 2 diabetes (T2DM), and other metabolic syndrome features. Reflecting the underlying pathogenesis and the cardiometabolic disorders associated with NAFLD, the term metabolic (dysfunction)-associated fatty liver disease (MAFLD) has recently been proposed. Indeed, over the past few years, growing evidence supports a strong correlation between NAFLD and increased cardiovascular disease (CVD) risk, independent of the presence of diabetes, hypertension, and obesity. This implies that NAFLD may also be directly involved in the pathogenesis of CVD. Notably, liver sinusoidal endothelial cell (LSEC) dysfunction appears to be implicated in the progression of NAFLD via numerous mechanisms, including the regulation of the inflammatory process, hepatic stellate activation, augmented vascular resistance, and the distortion of microcirculation, resulting in the progression of NAFLD. Vice versa, the liver secretes inflammatory molecules that are considered pro-atherogenic and may contribute to vascular endothelial dysfunction, resulting in atherosclerosis and CVD. In this review, we provide current evidence supporting the role of endothelial cell dysfunction in the pathogenesis of NAFLD and NAFLD-associated atherosclerosis. Endothelial cells could thus represent a "golden target" for the development of new treatment strategies for NAFLD and its comorbid CVD.

Antigen Cross-Presentation by Murine Proximal Tubular Epithelial Cells Induces Cytotoxic and Inflammatory CD8+ T Cells

Immune-mediated glomerular diseases are characterized by infiltration of T cells, which accumulate in the periglomerular space and tubulointerstitium in close contact to proximal and distal tubuli. Recent studies described proximal tubular epithelial cells (PTECs) as renal non-professional antigen-presenting cells that stimulate CD4⁺ T-cell activation. Whether PTECs have the potential to induce activation of CD8⁺ T cells is less clear. In this study, we aimed to investigate the capacity of PTECs for antigen cross-presentation thereby modulating CD8⁺ T-cell responses. We showed that PTECs expressed proteins associated with cross-presentation, internalized soluble antigen via mannose receptor-mediated endocytosis, and generated antigenic peptides by proteasomal degradation. PTECs induced an antigen-dependent CD8⁺ T-cell activation in the presence of soluble antigen in vitro. PTEC-activated CD8⁺ T cells expressed granzyme B, and exerted a cytotoxic function by killing target cells. In murine lupus nephritis, CD8⁺ T cells localized in close contact to proximal tubuli. We determined enhanced apoptosis in tubular cells and particularly PTECs up-regulated expression of cleaved caspase-3. Interestingly, induction of apoptosis in the inflamed kidney was reduced in the absence of CD8⁺ T cells. Thus, PTECs have the capacity for antigen cross-presentation thereby inducing cytotoxic CD8⁺ T cells in vitro, which may contribute to the pathology of immune-mediated glomerulonephritis.

Opportunities and Challenges for Nanotherapeutics for the Aging Population

Nanotherapeutics utilize the properties of nanomaterials to alter the pharmacology of the drugs and therapies being transported, leading to changes in their biological disposition (absorption, distribution, cellular uptake, metabolism and elimination) and ultimately, their pharmacological effect. This provides an opportunity to optimize the pharmacology of drugs, particularly for those that are dependent on hepatic action. Old age is associated with changes in many pharmacokinetic processes which tend to impair drug efficacy and increase risk of toxicity. While these age-related changes are drug-specific they could be directly addressed using nanotechnology and precision targeting. The benefits of nanotherapeutics needs to be balanced against toxicity, with future use in humans dependent upon the gathering of information about the clearance and long-term safety of nanomaterials.

Gut-liver-axis: Barrier function of liver sinusoidal endothelial cell

Liver diseases are associated with the leaky gut via the gut-liver-axis. Previous studies have paid much attention to the effect of gut barrier damage. Notably, clinical observations and basic research reveal that the gut barrier damage seldom leads to liver injury independently but aggravates pre-existing liver diseases such as non-alcoholic fatty liver disease and drug-induced liver injury. These evidences suggest that there is a hepatic barrier in the gut-liver-axis, protecting the liver against gut-derived pathogenic factors. However, it has never been investigated which type of liver cell plays the role of hepatic barrier. Under physiological conditions, liver sinusoidal endothelial cell (LSEC) can take up and eliminate virus, bacteriophage, microbial products, and metabolic wastes. LSEC also keeps the homeostasis of liver immune environment via tolerance-inducing and anti-inflammatory functions. In contrast, under pathological conditions, the clearance function of LSEC is impaired, and LSEC turns into a pro-inflammatory pattern. Given its anatomical position and physiological functions, LSEC is proposed as the hepatic barrier in the gut-liver-axis. In this review, we aim to further understand the role of LSEC as the hepatic barrier. Future studies are warranted to seek effective treatments to improve LSEC health, which appears to be a promising approach to prevent gut-derived liver injury.

Regulation and functional roles of chemokines in liver diseases

Inflammation is a major contributor to the pathogenesis of almost all liver diseases. Low-molecular-weight proteins called chemokines are the main drivers of liver infiltration by immune cells such as macrophages, neutrophils and others during an inflammatory response. During the past 25 years, tremendous progress has been made in understanding the regulation and functions of chemokines in the liver. This Review summarizes three main aspects of the latest advances in the study of chemokine function in liver diseases. First, we provide an overview of chemokine biology, with a particular focus on the genetic and epigenetic regulation of chemokine transcription as well as on the cell type-specific production of chemokines by liver cells and liver-associated immune cells. Second, we highlight the functional roles of chemokines in liver homeostasis and their involvement in progression to disease in both human and animal models. Third, we discuss the therapeutic opportunities targeting chemokine production and signalling in the treatment of liver diseases, such as alcohol-associated liver disease and nonalcoholic steatohepatitis, including the relevant preclinical studies and ongoing clinical trials.

Emerging Importance of Chemokine Receptor CXCR4 and Its Ligand in Liver Disease

Chemokine receptors are members of the G protein-coupled receptor superfamily, which together with chemokine ligands form chemokine networks to regulate various cellular functions, immune and physiological processes. These receptors are closely related to cell movement and thus play a vital role in several physiological and pathological processes that require regulation of cell migration. CXCR4, one of the most intensively studied chemokine receptors, is involved in many functions in addition to immune cells recruitment and plays a pivotal role in the pathogenesis of liver disease. Aberrant CXCR4 expression pattern is related to the migration and movement of liver specific cells in liver disease through its cross-talk with a variety of significant cell signaling pathways. An in-depth understanding of CXCR4-mediated signaling pathway and its role in liver disease is critical to identifying potential therapeutic strategies. Current therapeutic strategies for liver disease mainly focus on regulating the key functions of specific cells in the liver, in which the CXCR4 pathway plays a crucial role. Multiple challenges remain to be overcome in order to more effectively target CXCR4 pathway and identify novel combination therapies with existing strategies. This review emphasizes the role of CXCR4 and its important cell signaling pathways in the pathogenesis of liver disease and summarizes the targeted therapeutic studies conducted to date.

Role of liver sinusoidal endothelial cells in liver diseases

Liver sinusoidal endothelial cells (LSECs) form the wall of the hepatic sinusoids. Unlike other capillaries, they lack an organized basement membrane and have cytoplasm that is penetrated by open fenestrae, making the hepatic microvascular endothelium discontinuous. LSECs have essential roles in the maintenance of hepatic homeostasis, including regulation of the vascular tone, inflammation and thrombosis, and they are essential for control of the hepatic immune response. On a background of acute or chronic liver injury, LSECs modify their phenotype and negatively affect neighbouring cells and liver disease pathophysiology. This Review describes the main functions and phenotypic dysregulations of LSECs in liver diseases, specifically in the context of acute injury (ischaemia-reperfusion injury, drug-induced liver injury and bacterial and viral infection), chronic liver disease (metabolism-associated liver disease, alcoholic steatohepatitis and chronic hepatotoxic injury) and hepatocellular carcinoma, and provides a comprehensive update of the role of LSECs as therapeutic targets for liver disease. Finally, we discuss the open questions in the field of LSEC pathobiology and future avenues of research.

The role of liver sinusoidal endothelial cells in cancer liver metastasis

Liver sinusoidal endothelial cells (LSECs) are the gatekeeper cells in the liver, contributing critical roles in liver physiological and pathological changes. Factors such as dietary macronutrients, toxins, and aging impact LSEC fenestration. Defenestration of LSECs changes their phenotype and function. Under liver injury, capillarized LSECs promote hepatic stellate cells (HSCs) activation and fibrogenesis, while decapillarized LSECs protect the activation of HSCs and liver injury. The expression of chemokines, such as CXCL9 and CXCL16, changes and impacts the infiltration of immune cells in the liver during disease progression, including hepatocellular carcinoma (HCC). As the largest solid organ, liver is one of the most favorable organs into where tumor cells metastasize. The increased interaction and adhesion of circulating tumor cells (CTCs) with LSECs in the local microenvironment and LSEC-induced tolerance of immunity promote cancer liver metastasis. Several strategies can be applied to target LSEC to modulate their function to prevent cancer liver metastasis, including gut microbiota modulation, microRNA therapy, and medical treatment. Delivery of different treatment agents with nanoparticles may promote precise target treatment. Overall, targeting LSECs is a potential strategy for treatment of early liver diseases and prevention of cancer liver metastasis.

The Role of Sinusoidal Endothelial Cells in the Axis of Inflammation and Cancer Within the Liver

Liver sinusoidal endothelial cells (LSEC) form a unique barrier between the liver sinusoids and the underlying parenchyma, and thus play a crucial role in maintaining metabolic and immune homeostasis, as well as actively contributing to disease pathophysiology. Whilst their endocytic and scavenging function is integral for nutrient exchange and clearance of waste products, their capillarisation and dysfunction precedes fibrogenesis. Furthermore, their ability to promote immune tolerance and recruit distinct immunosuppressive leukocyte subsets can allow persistence of chronic viral infections and facilitate tumour development. In this review, we present the immunological and barrier functions of LSEC, along with their role in orchestrating fibrotic processes which precede tumourigenesis. We also summarise the role of LSEC in modulating the tumour microenvironment, and promoting development of a pre-metastatic niche, which can drive formation of secondary liver tumours. Finally, we summarise closely inter-linked disease pathways which collectively perpetuate pathogenesis, highlighting LSEC as novel targets for therapeutic intervention.

Liver sinusoidal endothelial cells - gatekeepers of hepatic immunity

Liver sinusoidal endothelial cells (LSECs) line the low shear, sinusoidal capillary channels of the liver and are the most abundant non-parenchymal hepatic cell population. LSECs do not simply form a barrier within the hepatic sinusoids but have vital physiological and immunological functions, including filtration, endocytosis, antigen presentation and leukocyte recruitment. Reflecting these multifunctional properties, LSECs display unique structural and phenotypic features that differentiate them from the capillary endothelium present within other organs. It is now clear that LSECs have a critical role in maintaining immune homeostasis within the liver and in mediating the immune response during acute and chronic liver injury. In this Review, we outline how LSECs influence the immune microenvironment within the liver and discuss their contribution to immune-mediated liver diseases and the complications of fibrosis and carcinogenesis.

Liver Sinusoidal Endothelial Cell: An Update

This update focuses on two main topics. First, recent developments in our understanding of liver sinusoidal endothelial cell (LSEC) function will be reviewed, specifically elimination of blood-borne waste, immunological function of LSECs, interaction of LSECs with liver metastases, LSECs and liver regeneration, and LSECs and hepatic fibrosis. Second, given the current emphasis on rigor and transparency in biomedical research, the update discusses the need for standardization of methods to demonstrate identity and purity of isolated LSECs, pitfalls in methods that might lead to a selection bias in the types of LSECs isolated, and questions about long-term culture of LSECs. Various surface markers used for immunomagnetic selection are reviewed.

Cytoplasm-Translocated Ku70/80 Complex Sensing of HBV DNA Induces Hepatitis-Associated Chemokine Secretion

Chronic hepatitis B virus (HBV) infection remains a serious disease, mainly due to its severe pathological consequences, which are difficult to cure using current therapies. When the immune system responds to hepatocytes experiencing rapid HBV replication, effector cells (such as HBV-specific CD8+ T cells, NK cells, NKT cells, and other subtypes of immune cells) infiltrate the liver and cause hepatitis. However, the precise recruitment of these cells remains unclear. In the present study, we found that the cytoplasm-translocated Ku70/80 complex in liver-derived cells sensed cytosolic HBV DNA and promoted hepatitis-associated chemokine secretion. Upon sensing HBV DNA, DNA-dependent protein kinase catalytic subunit and PARP1 were assembled. Then, IRF1 was activated and translocated into the nucleus, which upregulated CCL3 and CCL5 expression. Because CCR5, a major chemokine receptor for CCL3 and CCL5, is known to be critical in hepatitis B, Ku70/80 sensing of HBV DNA likely plays a critical role in immune cell recruitment in response to HBV infection.

Mouse Hepatitis Virus Infection Induces a Toll-Like Receptor 2-Dependent Activation of Inflammatory Functions in Liver Sinusoidal Endothelial Cells during Acute Hepatitis

Under physiological conditions, the liver sinusoidal endothelial cells (LSECs) mediate hepatic immune tolerance toward self or foreign antigens through constitutive expression of anti-inflammatory mediators. However, upon viral infection or Toll-like receptor 2 (TLR2) activation, LSECs can achieve proinflammatory functions, but their role in hepatic inflammation during acute viral hepatitis is unknown. Using the highly virulent mouse hepatitis virus type 3 (MHV3) and the attenuated variants 51.6-MHV3 and YAC-MHV3, exhibiting lower tropism for LSECs, we investigated in vivo and in vitro the consequence of LSEC infection on their proinflammatory profiles and the aggravation of acute hepatitis process. In vivo infection with virulent MHV3, in comparison to attenuated strains, resulted in fulminant hepatitis associated with higher hepatic viral load, tissue necrosis, and levels of inflammatory mediators and earlier recruitment of inflammatory cells. Such hepatic inflammatory disorders correlated with disturbed production of interleukin-10 (IL-10) and vascular factors by LSECs. We next showed in vitro that infection of LSECs by the virulent MHV3 strain altered their production of anti-inflammatory cytokines and promoted higher release of proinflammatory and procoagulant factors and earlier cell damage than infection by attenuated strains. This higher replication and proinflammatory activation in LSECs by the virulent MHV3 strain was associated with a specific activation of TLR2 signaling by the virus. We provide evidence that TLR2 activation of LSCEs by MHV3 is an aggravating factor of hepatic inflammation and correlates with the severity of hepatitis. Taken together, these results indicate that preservation of the immunotolerant properties of LSECs during acute viral hepatitis is imperative in order to limit hepatic inflammation and damage.

IMPORTANCE

Viral hepatitis B and C infections are serious health problems affecting over 350 million and 170 million people worldwide, respectively. It has been suggested that a balance between protection and liver damage mediated by the host's immune response during the acute phase of infection would be determinant in hepatitis outcome. Thus, it appears crucial to identify the factors that predispose in exacerbating liver inflammation to limit hepatocyte injury. Liver sinusoidal endothelial cells (LSECs) can express both anti- and proinflammatory functions, but their role in acute viral hepatitis has never been investigated. Using mouse hepatitis virus (MHV) infections as animal models of viral hepatitis, we report for the first time that in vitro and in vivo infection of LSECs by the pathogenic MHV3 serotype leads to a reversion of their intrinsic anti-inflammatory phenotype toward a proinflammatory profile as well to as disorders in vascular factors, correlating with the severity of hepatitis. These results highlight a new virus-promoted mechanism of exacerbation of liver inflammatory response during acute hepatitis.

Angiocrine signaling in the hepatic sinusoids in health and disease

The capillary network irrigating the liver is important not only for nutrient and oxygen delivery, but also for the signals distributed to other hepatic cell types necessary to maintain liver homeostasis. During development, endothelial cells are a key component in liver zonation. In adulthood, they maintain hepatic stellate cells and hepatocytes in quiescence. Their importance in pathobiology is highlighted in liver regeneration and chronic liver diseases, where they coordinate paracrine cell behavior. During regeneration, liver sinusoidal endothelial cells induce hepatocyte proliferation and angiogenesis. During fibrogenesis, they undergo morphological and functional changes, which are reflected by their role in hepatic stellate cell activation, inflammation, and distorted sinusoidal structure. Therapeutic strategies to target angiocrine signaling are in progress but are in the early stages. Here, we offer a short synthesis of recent studies on angiocrine signaling in liver homeostasis, regeneration, and fibrogenesis.

Scanning and transmission electron microscopy of the cells forming the hepatic sinusoidal wall of rat in acetaminophen and Escherichia coli endotoxin-induced hepatotoxicity

Drugs and xenobiotics as well as bacterial endotoxins may reach the liver either systematically or after intestinal absorption. Therefore, cells lining the sinusoidal wall form the last barrier before blood constituents get in contact with the parenchymal cells. In this work, the ultrastructure of the cells forming the sinusoidal wall was studied after acetaminophen and Escherichia coli endotoxin treatments. Rats received acetaminophen at a dose of 1000 mg/kg body weight by intraperitoneal injection once in acute and four times with a 1-week interval in chronic treatments, and E. coli endotoxin at a dose of 5 mg/kg of body weight by intraperitoneal injection once in acute and four times with a 1-week interval in chronic treatments. Tissue samples were collected for scanning and transmission electron microscopy. Swelling of sinusoidal endothelial cells was noticed in both acute intoxicated groups with narrowing of the fenestrae, whereas large gaps were formed in chronic toxicity. Activation of Kupffer cells was a prominent common feature between the four toxicity groups. Interestingly, hepatic stellate cell activation was evident in both chronic acetaminophen and chronic endotoxin groups. Large amounts of collagen fibers were seen surrounding the hepatic stellate cells and in Disse space.